1. Technical Field of the Invention
The invention relates to a plasma display panel, more specifically, to a plasma display panel having an improved plane electrode structure.
2. Related Art
The plasma display panel (xe2x80x9cPDPxe2x80x9d) is well known as a thin flat image display device having a large display screen and displaying a mass information. In the plasma display panel, electrons are accelerated by means of an electric field to cause them to collide with a discharged gas to excite it and convert ultraviolet light irradiated through a relaxation process of the exited gas into visible light to display images. Among various types, the alternating current (xe2x80x9cACxe2x80x9d) PDP is superior than the direct current (xe2x80x9cDCxe2x80x9d) PDP in terms of luminance, luminous efficiency and operating life.
An example of this type of AC type PDP is disclosed in Japanese Unexamined Patent Publication No. 149873 of 1999. FIG. 1 and FIG. 2 are both plan views of a unit cell (single color illuminating cell) portion of said PDP disclosed by said publication and correspond with FIG. 7 and FIG. 8 of said publication respectively. The constitution of the prior art will be describe below using FIG. 1 and FIG. 2.
On a back substrate 51, a plurality of metal data electrodes 52 are formed at a specified interval in the column direction, on top of which a white dielectric material layer 53 is formed. On the white dielectric material layer 53, located between the data electrodes 52, stripe partition walls 54 are formed at a specified interval in the column direction. Containing the side faces of said partition walls and on the white dielectric layer 53, a plurality of fluorescent material layers 55, each of which consists of a set of fluorescent material layers 55r, 55g and 55b, each of which generates visible red (r), green (g) and blue (b) light respectively, are formed repeatedly in the column direction.
On the other hand, beneath a front substrate 56, a plurality of stripe plane electrodes 57a are formed in pairs in the row direction at a specified interval forming a pair, below which a plurality of metallic bus electrodes 58 are formed at a specific interval in the row direction. Beneath the stripe plane electrodes 57a and the bus electrode 58, a transparent dielectric layer 61 is formed, under which is formed a protection layer 62. The stripe plane electrode 57a and the bus electrode 58 form a pair of sustaining electrodes consisting of a scan electrode 59 and a common electrode 60.
Said back substrate 51 and said front substrate 56 are put together sandwiching their constituents inside and are sealed air tight with a sealing part provided on the periphery of the substrate. A discharged gas consisting of gaseous atoms and gaseous molecules for generating ultraviolet light is encapsulated in the inside of the above.
Next, let us describe the operating principle of the prior art. Writing discharge is created by causing an opposing discharge between a data electrode 52, to which signal voltage pulses are applied independently by each line, and a scan electrode 59, to which write voltage pulses are applied due to line sequential scanning, in order to generate wall electric charges and priming particles (electrons and ions) to perform a cell selecting operation. The selected cell generates a sustaining discharge by means of a plane discharge between the scanning electrode 59, to which a sustaining voltage is applied following the writing voltage pulses, and the common electrode 60, in order to cause visible light luminescence of the fluorescent material layers 55 to operate the cell to display.
In the conventional structure shown in FIG. 1 and FIG. 2, since the stripe plane electrode 57a is formed in a wide range over a plurality of cells, there was a problem in that the sustaining current (current that runs in accordance with the sustaining discharge), which runs in proportion to the sustaining electrode area, is too large causing large power consumption. When the power consumption is large, it creates not only a large load on the drive circuit, but also an increase in heat generation of the panel, thus resulting in the problem of reliability.
Furthermore, the conventional structure shown in FIG. 1 and FIG. 2 tends to cause a spread of plasma into adjacent cells in vertical and horizontal directions as a result of discharge, thus creating a problem of incorrect light turn on and turn off due to discharge interferences between adjacent cells.
A countermeasure normally taken to cause a selected cell to perform a luminescence display uniformly over the entire panel surface is to generate a strong discharge by increasing the writing voltage (potential difference that can cause writing discharge between a data electrode 52 and a scan electrode 59) and the sustaining voltage (potential difference that can cause sustaining discharge between a scan electrode 59 and a common electrode 60) to high levels, thus generating more wall charges and priming particles so that the capability of transition from writing operations to sustaining operations can be improved. However, if discharge interferences can easily occur between adjacent cells, it is impossible to increase the writing voltage and the sustaining voltage because incorrect light turn on and turn off discharges occur at unselected cells adjacent to the selected cell and cause the unselected cells to turn on and turn off incorrectly when high discharges are caused by increasing the writing voltage and the sustaining voltage to high levels. As a result, the PDP""s display image quality seriously deteriorates.
On the other hand, lowering of the writing voltage and the sustaining voltage in order to suppress the discharge interferences between adjacent cells deteriorates the capability making a transition from the writing operation to the sustaining operation and makes it impossible to perform a normal luminescence display, hence also deteriorating the PDP""s display image quality. In other words, it was impossible to expand the operating margin and improve the display image quality with the conventional structure shown in FIG. 1 and FIG. 2.
In order to solve the above problem, a PDP with the structure disclosed by the Japanese Unexamined Patent Publication No. 22772 of 1996 was proposed. FIG. 3 and FIG. 4 are both the plan views of a unit cell portion of said PDP disclosed by said publication and correspond with the constitutions shown in FIG. 7(b) and FIG. 7(a) of said publication respectively.
In the conventional structure shown in FIG. 3, plane electrodes 57b are formed by means of rectangular transparent electrodes disposed in each unit cell and these rectangular plane electrodes 57b are connected by bus electrodes 58 provided on the side of non-discharging gaps 64 in the row direction to form a pair of sustaining electrodes (scan electrode 59 and common electrode 60). On the other hand, in the conventional structure shown in FIG. 4, plane electrodes 57c are formed by means of T-shaped transparent electrodes disposed in each unit cell and these T-shaped plane electrodes 57c are connected by bus electrodes 58 provided on the side of non-discharging gaps 64 in the row direction to form a pair of sustaining electrodes (scan electrode 59 and common electrode 60). As to the bus electrodes 58, there is no mention of them in FIG. 7(b) and FIG. 7(a) of the Japanese Unexamined Patent Publication No. 22772 of 1996, but it was described in the above assuming that the bus electrodes 58 exist as in the structure of the conventional PDP.
In the conventional structures shown in FIG. 3 and FIG. 4, the sustaining current is reduced by reducing the sustaining electrode area compared to that of the conventional structure shown in FIG. 2 by means of providing the plane electrodes 57b and 57c independently in each unit cell. Furthermore, by optimizing the length of the plane electrodes (forming the discharge gap 63) in the column direction and the length of the plane electrodes in the row direction, the discharge starting voltage is reduced in order to reduce the consumption voltage while maximizing the luminous efficiency. In particular, in the case of the conventional structure shown in FIG. 4, the power consumption can be substantially reduced from the conventional structure shown in FIG. 2, so that the heat generation per unit cell can be reduced as well. These features are described in paragraphs No. [0019], [0025] and [0026] of the Japanese Unexamined Patent Publication No. 22772 of 1996 respectively.
In order to solve the above problem, a PDP with the structure disclosed by the Japanese Unexamined Patent Publication No. 250030 of 1996 was proposed. FIG. 5 and FIG. 6 are both the plan views of a unit cell portion of said PDP disclosed by said publication and correspond to the constitutions shown in FIG. 2 and FIG. 4 of said publication respectively.
In the conventional structure shown in FIG. 5, transparent electrodes (transparent conducting films) 72 of the sustaining electrodes 72A that form a sustaining electrodes pair have protruding parts 72a opposing each other in each cell and the bus electrodes (metallic film) 73 are provided to cross over inside parts 72b of the transparent electrodes 72, thus partially covering the protruding parts 72a of the transparent electrodes 72, and providing a boundary resistance in each cell independently between base areas 72c of the protruding parts 72a and the bus electrodes 73. On the other hand, the conventional structure shown in FIG. 6 shows a case where the protruding parts 72a of the transparent electrodes 72 are made narrower than the widths of heads 72e also forming T-shapes. According to the structure shown in FIG. 6, as the areas of the protruding parts 72a are smaller than in those of the sustaining electrodes 72A shown in FIG. 5, the discharge current can be further reduced.
The transparent electrodes 72 are made of ITO (indium tin oxide) or SnO2 (tin oxide), and the bus electrodes 73 are made of Al (aluminum) or Al alloy. Data electrodes 79 are provided in such a way as to cross over the sustaining electrodes 72A.
In the conventional structures shown in FIG. 5 and FIG. 6, the bus electrodes 73 are made of low resistance Al or Al alloys in order to alleviate the waveform dulling of voltage pulses that can be caused by voltage drops, so that the drive margin can be improved and luminance variation can be suppressed. Moreover, the peak value of the sustaining current is reduced to enable the consumption current to be reduced by providing a boundary resistance in each cell independently between the base areas 72c of the protruding parts 72a of the transparent electrodes 72 and the bus electrodes 73. Furthermore, since the partition walls 72a of the transparent electrodes 72, which correspond to the plane electrodes 57a, do not exist in the areas that correspond to the partition walls 54 shown in FIG. 1 and FIG. 2, it is claimed that error discharges between the horizontally adjacent cells can be reduced. These features are described in the paragraphs No. [0025], [0026] and [0028] of the Japanese Unexamined Patent Publication No. H8(1996)-250030 respectively.
However, the conventional PDPs described in the above publications have the following problems.
First, although the conventional structure shown in FIG. 3 disclosed by the Japanese Unexamined Patent Publication No. 8-22772 of 1996 succeeds in making the plasma generated by the sustaining discharge extend thick and long thus resulting in a high luminance, it has a problem in that its sustaining electrode surface is wider so that its luminous efficiency is lower as the sustaining current is larger than the conventional structure shown in FIG. 4 disclosed by the Japanese Unexamined Patent Publication No. 8-22772 of 1996.
Next, although the conventional structure shown in FIG. 4 provides a higher luminous efficiency as the plasma generated by the sustaining discharge extends thin and long, it has a problem in that it produces less sustaining current compared to the conventional structure shown in FIG. 3, so that its luminance is lower. In other words, neither the conventional structure shown in FIG. 3 nor the one shown in FIG. 4 can have both a high luminance and a high luminous efficiency simultaneously.
The conventional structure shown in FIG. 3 has a further problem that the plasma generated by the sustaining discharge has a stronger tendency to spread in the vertical and horizontal directions than the conventional structure shown in FIG. 4, and tends to cause light to turn on and turn off incorrectly due to discharge interferences between adjacent cells.
Moreover, the conventional structures shown in FIG. 3 and FIG. 4 including the conventional structures shown in FIG. 5 and FIG. 6 disclosed in the Japanese Unexamined Patent Publication No. 8-250030 of 1996 have such reliability problems in that the Al electrodes (e.g., bus electrodes 58) get peeled off partially or totally from the transparent electrodes (e.g., plane electrodes 57b, 57c) during manufacturing processes, and the Al electrodes separate from the transparent electrodes partially or totally during the panel operation so that poor continuity occurs between them. And disappearance of the Al electrodes and the transparent electrodes themselves due mainly to galvanic cell corrosion between them during the patterning process of the Al electrodes.
It is well known that the presence of the Al electrodes that are generally apt to produce oxides and the transparent electrodes which are essentially oxides, which contact each other, may cause various problems. This is due to the fact that Al2O3 (aluminum oxide) is thermodynamically less stable than, for example, In2O3 (indium oxide) or SnO2 (tin oxide). As a result, a reduction reaction of the transparent electrode occurs in accordance with oxidation of the Al electrode on the interface between the Al electrode and the transparent electrode, which leads to an increase of electrical resistance with formation of an insulation film and an increase of the boundary level. This is the reason why a boundary resistance is formed in the technology disclosed by the Japanese Unexamined Patent Publication No. 8-250030 of 1996.
The above-mentioned reactions can be further accelerated when thermal energy is added and develops a blackening phenomenon as a result of the reduction of the transparent electrodes. This is due to the fact that metal elements are precipitated as a result of the reduction of the transparent electrodes, which are essentially oxides, and it reduces the transmittance of the transparent electrodes and consequently their luminance.
Moreover, the boundary condition becomes sparse due to the oxidation/reduction reactions between the Al electrodes and the transparent electrodes, causing the problem of the Al electrodes that are used as the bus electrodes 58 peeling off from the transparent electrodes used as the plane electrodes 57b and 57c. Since the bus electrodes 58 are provided to reduce the wavy dulling of the voltage pulses and to apply the specified voltage pulses to the plane electrodes 57b and 57c disposed in each cell, this is a major problem for the panel operation.
Furthermore, in the process of etching and patterning the Al electrodes using a positive type photo resist as a mask, the Al electrodes can get corroded by the organic alkali developing liquid used for developing the positive type photo resist, so that pinholes can be generated on the Al electrodes. When the developing liquid (electrolytic solution) reaches the transparent electrodes through these pinholes, an electric circuit will be established between the Al electrodes and the transparent electrodes via the developing liquid, and dissolution (oxidation) of the Al electrodes and disappearance (reduction) of the transparent electrodes occur caused by the oxidation/reduction potential difference as the driving force. This phenomenon is known as a galvanic cell corrosion reaction, and it eventually causes both the Al electrodes and the transparent electrodes disappear or severely deteriorate their performances as the electrodes.
This is caused by the fact that the oxidation/reduction potential of the Al electrode is on the base metal side compared to the transparent electrode (the oxidation/reduction potential of the transparent electrode is on the noble metal side compared to the Al electrode), hence causing the electrons generated during the oxidation of the Al electrodes to flow into the transparent electrodes, and the incoming electrons reduce the transparent electrodes. Also, the oxidation/reduction reaction caused by this potential difference as a driving force is more serious than the one caused by the heat as the driving force. It comes from the fact that the corrosion reaction is an electrochemical reaction.
The object of the invention is to provide an AC plane discharge type plasma display panel with a broader operating margin and a lower power consumption rate by means of achieving a higher luminance and a higher luminous efficiency simultaneously and suppressing the incorrect light turn on and turn off due to discharge interferences between adjacent cells.
An AC plane discharge type plasma display panel according to claim 1, comprises: a front substrate provided with at least a plurality of double sided electrodes that extend in the row direction; and a back substrate provided with at least a plurality of data electrodes that extend in the column direction. Said substrates are arranged to face to each other forming a discharge space theirbetween into which a gas for generating ultraviolet light is introduced and sandwiching partition walls that separate unit illuminating pixels each of which has a fluorescent material layer that emits a visible light of a desired color Said double sided electrodes consist of bus electrodes that extend in said row direction and plane electrodes electrically connected with said bus electrodes. Said plane electrodes consist of discharge sections that are divided spatially into a plurality of regions.
An AC plane discharge type plasma display panel according to claim 2 comprises: a front substrate provided with a plurality of pairs of a scan electrode and a common electrode that extend in the row direction: and a back substrate provided with a plurality of data electrodes that extend in the column direction. Said substrates are arranged to face to each other forming a discharge space theirbetween into which a gas for generating ultraviolet light is introduced and sandwiching partition walls that separate unit illuminating pixels each of which has a fluorescent material layer that emits visible light of a desired color. Said scan electrodes and said common electrodes consist of bus electrodes that extend in said row direction and plane electrodes electrically connected with said bus electrodes. Said plane electrodes consist of discharge sections that are divided spatially into a plurality of regions.
Said fluorescent material layers may consist of a plurality of kinds that emit visible lights of red, green and blue.
Plane electrodes of discharge cells having at least one kind of said a plurality of fluorescent material layers may have a different shape from plane electrodes of discharge cells that have other fluorescent material layers.
Said plane electrodes may be provided for each of said unit illuminating pixels independently.
The density of said divided discharge sections that constitute said plane electrode may stay constant from the row direction center axis of said unit illuminating pixels toward outside.
The density of said divided discharge sections that constitute said plane electrode may increase from the row direction center axis of said unit illuminating pixels toward outside.
The density of said divided discharge sections that constitute said plane electrode may decrease from the row direction center axis of said unit illuminating pixels toward outside.
The density of said divided discharge sections that constitute said plane electrode may stay constant from the column direction center axis of said unit illuminating pixels toward outside.
The density of said divided discharge sections that constitute said plane electrode may increase from the column direction center axis of said unit illuminating pixels toward outside.
The density of said divided discharge sections that constitute said plane electrode may decrease from the column direction center axis of said unit illuminating pixels toward outside.
The density of said divided discharge sections that constitute said plane electrode may stay constant from the row direction center axis of said unit illuminating pixels toward outside and from the column direction center axis of said unit illuminating pixels toward outside.
The density of said divided discharge sections that constitute said plane electrode may increase from the row direction center axis of said unit illuminating pixels toward outside and from the column direction center axis of said unit illuminating pixels toward outside.
The density of said divided discharge sections that constitute said plane electrode may decrease from the row direction center axis of said unit illuminating pixels toward outside and from the column direction center axis of said unit illuminating pixels toward outside.
The plane electrodes may consist of a plurality of thin wire electrodes extending in the row direction, which are disposed in such a way that their intervals expand at a specific rate from a discharge gap section to a non-discharge gap section, while the lengths of said thin electrodes shorten with a specific difference from said discharge gap section to said non-discharge gap section.
Said plurality of thin wire electrodes extending in said row direction may be connected to said bus electrodes via thin wire electrodes extending in the column direction.
Said bus electrodes that extend in said row direction may be disposed between vertically adjacent discharge cells and said plane electrodes extend from said bus electrodes to the vertically discharge cells.
Said bus electrodes may be made of a metal or alloy and said plane electrodes may be made of a transparent electric conductive material.
Said bus electrodes may be made of a metal or alloy and said plane electrodes may be made of a metal or alloy which is the same material to or the different material from the bus electrodes.
The thickness of said plane electrodes may be between 5 nm and 50 nm.
Each of said double sided electrode, said scan electrode, said common electrode and said data electrode has a single layer structure or a multi-layer structure at least partially consisting of one or more of the following substances: Au or Au alloy, Ag or Ag alloy, Cu or Cu alloy, Al or Al alloy, Cr or Cr alloy, Ni or Ni alloy, Ti or Ti alloy, Ta or Ta alloy, Hf or Hf alloy, Mo or Mo alloy, or W or W alloy.
According to the plasma display panel of this invention, the plane electrodes, where lines of electric force are generated, are formed by micro discharge sections spatially divided into several regions, so that plasma can be expanded into the entire cell with a necessary and sufficient electrode surface, so that it is possible to reduce the power consumption substantially, making it possible to substantially improve luminance and luminous efficiency of the conventional PDP.
Furthermore, according to the plasma display panel of this invention, the density of the lines of electric force is designed to reduce from the discharge gap section to the non-discharge gap section as well as from the cell""s vertical center axis to the partition wall part, not only the performance of transition from the writing operation to the sustaining operation can be improved, but also the discharge interferences between the vertically and horizontally adjacent cells can be more effectively suppressed, so that the operation margin can be widened. As a result, a better image quality can be achieved.
Furthermore, according to the plasma display panel of this invention, the density of the lines of electric force is designed to increase from the discharge gap section to the non-discharge gap section as well as from the cell""s vertical center axis to the partition wall part, the plasma generated by the sustaining discharge in the discharge gap section can be extended more easily into the entire cell, so that the entire fluorescent layer can be irradiated with the ultraviolet light more uniformly, thus improving luminance and luminous efficiency.
Furthermore, according to the plasma display panel of this invention, the density of the lines of electric force is designed to decrease in a fan shape from the discharge gap section to the non-discharge gap section, it is possible to satisfy both the illuminating characteristics (luminance and luminous efficiency) and the voltage characteristics (transition from the writing operation to the sustaining operation and discharging interferences between adjacent cells). As a result, it is possible to reduce the power consumption more than in any other PDPs known so far, and widen the operating margin.